<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"%>
<%
	// 在内存中创建图象 
	int width = 60, height = 20;
	BufferedImage image = new BufferedImage(width, height,
			BufferedImage.TYPE_INT_RGB);

	// 获取图形上下文 
	Graphics g = image.getGraphics();

	// 设定背景色 
	g.setColor(new Color(0xDCDCDC));
	g.fillRect(0, 0, width, height);

	//画边框 
	g.setColor(Color.black);
	g.drawRect(0, 0, width - 1, height - 1);

	// 随机产生的认证码(4位数字) 
	String rand = "" + (Math.random() * 10000);
	rand = rand.substring(0, rand.indexOf("."));
	switch (rand.length()) {
	case 1:
		rand = "000" + rand;
		break;
	case 2:
		rand = "00" + rand;
		break;
	case 3:
		rand = "0" + rand;
		break;
	default:
		rand = rand.substring(0, 4);
		break;
	}

	// 将认证码存入SESSION 
	session.setAttribute("rand", rand);

	// 将认证码显示到图象中 
	g.setColor(Color.black);
	Integer tempNumber = new Integer(rand);
	String numberStr = tempNumber.toString();

	g.setFont(new Font("Atlantic Inline", Font.PLAIN, 18));
	String Str = numberStr.substring(0, 1);
	g.drawString(Str, 8, 17);

	Str = numberStr.substring(1, 2);
	g.drawString(Str, 20, 15);
	Str = numberStr.substring(2, 3);
	g.drawString(Str, 35, 18);

	Str = numberStr.substring(3, 4);
	g.drawString(Str, 45, 15);

	// 随机产生88个干扰点，使图象中的认证码不易被其它程序探测到 
	Random random = new Random();
	for (int i = 0; i < 20; i++) {
		int x = random.nextInt(width);
		int y = random.nextInt(height);
		g.drawOval(x, y, 0, 0);
	}

	// 图象生效 
	g.dispose();

	// 输出图象到页面 
	ImageIO.write(image, "JPEG", response.getOutputStream());
	//在页面上调用  <img src="/yourPath/checkNum.jsp" />
%>
